Method of recovering chrome from a tannery process

ABSTRACT

A system and method for a chromium recovery process for recovering chromium from byproducts resulting from a tannery process. A system and process for solubilizing chromium contained in the oil byproduct into the remaining water content within the oil and extracting the water from the oil with the chromium sufficiently solubilized in the water such that the chromium content in the oil is sufficiently reduced below hazardous levels.

BACKGROUND

1. Field

This technology relates generally to the tanning process and, moreparticularly, to recovery of chrome from a tannery process.

2. Background Art

Tanning, sometimes referred to as “tannery process”, is the process oftreating the skin of an animal to produce leather, which is more durableand less susceptible to decomposition, and which is conducive for use inclothing or furnishing product or other covering items. Traditionally,tanning used tannin, an acidic chemical compound found in oak and firtrees from which the tanning process draws its name. A tannery is theterm for a place where the skins are processed, hence, the reason forwhy the process is also referred to “tannery process”.

Tanning leather is a process which permanently alters the proteinstructure of skin. Making “rawhide” (untanned but worked hide) does notrequire the use of tannin. Rawhide is made by removing the flesh and fatand then the hair by use of an aqueous solution (this process is oftencalled “liming” when using lime and water or “bucking” when using woodash (lye) and water), then scraping over a beam with a somewhat dullblade, then drying. These methods for removing the hair can also act toclean the skin prior the tanning process to allow for penetration andaction of the tanning agent, so that all the steps in preparation ofrawhide except drying are often precursors to the more complex processof tanning and production of leather.

Tanning can be performed with either vegetable or mineral methods.Before tanning, the skins have the hair removed as discussed above,degreased, desalted and soaked in water over a period that can last upto about approximately 2 days. To prevent damage of the skin bybacterial growth during the soaking period, biocides can be utilized.Fungicides can also be used in the process to protect wet leathers frommold growth.

An animal can be killed and skinned before the body heat leaves thetissues and the skin can be sent on to the tannery. This can be done bythe tanner, or by obtaining a skin from a rendering facility or a farmwhere the animals are grown. Preparing hides begins by curing them withsalt. Curing is employed to prevent putrefaction of the proteinsubstance (collagen) from bacterial growth during the time lag thatmight occur from procuring the hide to when it is processed. Curingremoves excess water from the hides and skins using a difference inosmotic pressure. The moisture content of hides and skins gets greatlyreduced. In wet-salting, the hides are heavily salted, then pressed intopacks for about 30 days. In brine-curing the hides are agitated in asalt water bath for about 16 hours. The steps in the production ofleather between curing and tanning are collectively referred to asbeamhouse operations. They include, in order, soaking, liming, removalof extraneous tissues (unhairing scudding, and fleshing), deliming,bating, drenching, and pickling.

The Chromium(III) sulfate ([Cr(H₂O)₆]₂(SO₄)₃) type tannery process isregarded as an efficient and effective tanning process. Chromium(III)compounds of the sort used in tanning are significantly less toxic thanhexavalent chromium. Chromium(III) sulfate dissolves to give thehexaaquachromium(III) cation, [Cr(H₂O)₆]³⁺, which at higher pH undergoesprocesses called oblation to give polychromium(III) compounds that areactive in tanning—being the cross-linking of the collagen subunits. Thechemistry of [Cr(H₂O)₆]³⁺ is more complex in the tanning bath ratherthan in water due to the presence of a variety of ligands. Some ligandsinclude the sulfate anion, the collagen's carboxyl groups, amine groupsfrom the side chains of the amino acids, as well as “masking agents.”Masking agents are carboxylic acids, such as acetic acid, used tosuppress formation of polychromium(III) chains. Masking agents allow thetanner to further increase the pH to increase collagen's reactivitywithout inhibiting the penetration of the chromium(III) complexes.

Collagen is characterized by a high content of glycine, proline, andhydroxprolene, usually in the repeat -gly-pro-hypro-gly. These residuesgive rise to collagen's helical structure. Collagen's high content ofhydroxyproline allows for significant cross-linking by hydrogen bondingwithin the helical structure. Ionized carboxyl groups (RCO₂ ⁻) areformed by hydrolysis of the collagen by the action of hydroxide. Thisconversion occurs during the liming process, before introduction of thetanning agent (chromium salts). The ionized carboxyl groups coordinateas ligands to the chromium(III) centers of the oxo-hydroxide clusters.Tanning increases the spacing between protein chains in collagen from 10to 17 Å. The difference is consistent with cross-linking by polychromiumspecies, of the sort arising from olation and oxolation.

Subsequent to application of the chromium agent, the bath is treatedwith sodium bicarbonate to increase the pH to 4.0-4.3. This increaseinduces cross-linking between the chromium and the collagen. The pHincrease is normally accompanied by a gradual temperature increase up to40° C. Chromium's ability to form such stable bridged bonds explains whyit is considered one of the most efficient tanning compounds.Chromium-tanned leather can contain between 4 and 5% of chromium. Thisefficiency is characterized by its increased hydrothermal stability ofthe skin, and its resistance to shrinkage in heated water.

However, one down side to the chromium tanning process is the byproducts that are produced that have to be safely disposed of.Byproducts of the tanning process include some small solids, water andoil. Each of these by products can contain residual chromium that is atsufficiently high levels that it requires special hazardous wastedisposal in order to safely dispose of the byproduct. The lack of theability to safely extract and dispose of larger amounts of water and thelack of the ability to recover the chromium from larger amounts of thewater in order to reuse the chromium and easily dispose of the waterwithout hazardous waste handling measures creates a burden and cost forthe tannery process. The result of the lack of ability to recover largeramounts of water from the oil byproduct is the inability to recoverchromium from the oil byproduct such that the chromium lever issufficient low to safely reuse the oil, which means that the oil has tobe disposed of under certain hazardous waste standards, which can becostly.

BRIEF SUMMARY

The invention is a chromium recovery process for recovering chromiumfrom byproducts resulting from a tannery process. The waste byproductsfrom a tannery process can typically be stored in large storage drums ortanks for a period of time, which results in a three phase byproductthat includes small solids which settle to the bottom of the tank and anoil byproduct that rises to the top of the tank and water is suspendedthere between. The three phase separation is simply the result ofgravity and the varying density of the different phases of thebyproduct. All three phases of the byproduct can contain residualamounts of chromium at levels that require special hazardous wastedisposal. The invention includes a process for solubilizing chromiumcontained in the oil byproduct into the remaining water content withinthe oil and extracting the water from the oil with the chromiumsufficiently solubilized in the water such that the chromium content inthe oil is sufficiently reduced below hazardous levels. The invention isa system and process for recovering chromium that allows greaterportions of the chromium separated from the oil to be reused in atanning process because it allows more water and soluble chrome to beremoved from the oil and therefore a greater amount of water can beprocessed to have sufficiently low chromium levels to be readilydisposed of as waste water and allows the oil to have chromium levelsless than five (5) parts per million such that the oil can be recycledfor reuse such as for biodiesel.

The system includes large storage tanks or drums for holding thebyproduct from the chrome tannery process. The tanks are used to storethe product until separation occurs where the byproduct separates intothree phases based on varying density and gravity. Solids settle to thebottom of the tank and oil rises to the top and blue water (watercontaining chromium) is suspended there between. This three phaseseparation process can take from about approximately 10 to 12 hours. Askimmer is used to skim the oil from the top portion of the three phasebyproduct. Decanting can also be utilized. The water is decanted off orpumped/poured off and the solids are pumped off. The oil and the solidsare fed to a tank with a mechanical stirrer and steam sparge (a steamsparge mixer) that provides low viscosity turbulent flow mixing and themixture is heated from ambient temperature to about 180 degrees to about200 degrees Fahrenheit. The steam sparged process can last for aboutapproximately six (6) hours.

The steam sparged mixture is pumped into a three phase centrifuge, whichseparates the solids, oil and water in one step. Therefore, additionalwater is removed from the oil and solids that can be processed forremoving chrome. The water reduced solids are appropriately disposed of.The oil is feed into an agitator where the oil is agitated and a 4%-5%acid wash is performed. The agitation is provided for adequate mixingand to assist in the reaction of the chrome and the acid where thechrome is solubilized in the water still within the oil. When theagitation stops, the oil and water will separate. The water can bedecanted off and the oil can be heated from about 180 degrees to about205 degrees to about 210 degrees Fahrenheit and feed into a clarifier ora vertical disc type centrifuge where water remaining in oil is removed.The acid wash and heating can last for approximately two (2) hours.

The oil should now have sufficiently low chromium such that it can bereused. The water throughout the process that is drained off can beprecipitated to remove the chrome and the chrome can be reused fortanning and the water can be disposed of as normal non-hazardous wastewater.

These and other advantageous features of the present invention will bein part apparent and in part pointed out herein below.

BRIEF DESCRIPTION OF THE DRAWINGS

For a better understanding of the present invention, reference may bemade to the accompanying drawings in which:

FIG. 1 is a functional diagram of the system and process.

While the invention is susceptible to various modifications andalternative forms, specific embodiments thereof are shown by way ofexample in the drawings and will herein be described in detail. Itshould be understood, however, that the drawings and detaileddescription presented herein are not intended to limit the invention tothe particular embodiment disclosed, but on the contrary, the intentionis to cover all modifications, equivalents, and alternatives fallingwithin the spirit and scope of the present invention as defined by theappended claims.

DETAILED DESCRIPTION OF INVENTION

According to the embodiment(s) of the present invention, various viewsare illustrated in FIG. 1 and like reference numerals are being usedconsistently throughout to refer to like and corresponding parts of theinvention for all of the various views and FIGURES of the drawing. Also,please note that the first digit(s) of the reference number for a givenitem or part of the invention should correspond to the FIGURE number inwhich the item or part is first identified.

One embodiment of the present technology comprising a three phasedecanter, an acid wash agitator and a clarifier teaches a novelapparatus and method for recovering chrome from oil byproduct of atannery process.

The details of the invention and various embodiments can be betterunderstood by referring to the FIGURES of the drawing. Referring to FIG.1, a system and process is illustrated for recovering chrome from oilbyproduct. The byproduct from the chrome tannery process is stored in alarge settling tank as illustrated by 102. The byproduct is allowed toform a three phase system due to gravity and the varying density of thethree different phases. The oil byproduct 104 phase will rise to the topof the three phase byproduct. The solid byproduct 106 phase will settleto the bottom and the water byproduct 108 phase will be suspendedbetween the oil byproduct phase and the solid byproduct phase. The oilbyproduct is skimmed from the top and pumped 110 into a steam spargingmixer. The oil byproduct that is skimmed from the settling tank cantypically have greater than 10,000 parts-per-million (ppm) Chromium. Thewater is decanted off and the solid byproduct is pumped 112 into thesteam sparging mixer 114. The steam sparging mixer has a mixing element116 for mixing the byproducts and a steam infuser 118 for providingturbulent flow mixing. The steam sparge raises the temperature fromambient to about 180 degrees to about 200 degrees Fahrenheit.

The system provides steam sparging and mixing of the oil and solidbyproducts from a chrome tannery process forming a steam spargedmixture. The steam sparged mixture is steam infused, heated and pumped120 into a three phase centrifuge 121 for separating out a separated oil122 byproduct. The chrome content of the oil byproduct after the 3-phaseseparation can be about approximately less than 15,000 ppm. Theseparated oil byproduct is pumped 124 to an acid wash agitator vessel126 having an agitator and an acid dispensing mechanism. The three phaseseparated oil 122 byproduct is acid washed and agitated. The agitationcan be ceased which allows an acid washed oil 128 byproduct to separate.The acid washed oil can have about approximately less than 50 ppm. Theacid washed oil 128 can be pumped 130 to a heating vessel and clarifiersystem 132. The step of heating the acid washed oil byproduct andremoving water from the acid washed oil byproduct can be performed usinga clarifier 134 forming a clarified oil 136 byproduct. The clarified oilcan be captured for reuse 138. The clarified oil can have a chromecontent of about approximately less than 1 ppm.

When heating the steam sparged mixture it can be heated from aboutapproximately ambient to 180 degrees to about approximately 200 degreesFahrenheit. The process of acid washing is about four (4) percent toabout five (5) percent acid washing. The process of heating the acidwashed oil byproduct can be heating from about 170 degrees to 190degrees Fahrenheit to about 205 degrees to about 210 degrees Fahrenheit.When clarifying the acid washed oil byproduct the clarifier can be adisc type vertical centrifuge. The captured clarified oil byproduct canhave less than five (5) parts per million chromium.

The steam sparging mixer can have a steam sparger input port 142communicably connected to a tannery process byproduct settling tank 102and operable to receive oil byproduct and solids byproduct from thetannery process byproduct settling tank into the steam sparging mixer,and said steam sparging mixer can have a steam sparger for mixing andheating the oil byproduct and the solid byproduct and the steam spargingmixer can have an output pump 144 communicably connected and adapted topump a mixed steam sparged byproduct into a three (3) phase centrifuge.

The acid wash agitation vessel can have an agitator and an acid infuserand the agitation vessel can have an output pump and can be communicablyconnected for flowing acid washed oil to a heater and clarifier. Heatingthe steam sparging mixture with the steam sparger and mixer can beadapted to heat contents from less than or equal to 180 degreesFahrenheit to about 180 degrees to about 200 degrees Fahrenheit. Theacid washing agitator vessel can adapted to provide about four (4)percent to about five (5) percent acid washing. When heating the acidwashed oil byproduct it can be heated from about 205 degrees to about210 degrees Fahrenheit. The clarifier can be a disc type verticalcentrifuge.

A testing an analysis was performed utilizing the Chrome Recoveryprocess as outlined herein and the following illustrates the results.

DC Hides/Tanner Chrome Grease Project—Testing and Analysis Background:

The Raw Grease collected by the DC Hides/Tannery (which consists of TopGrease, Bottom Solids, and Blue Water)collected, mixed, heated to 180°-200° F., and then pump through ourP-35000 3-Phase centrifuge.The 3-Phase will separate the solids, water, and oil. The solids will becollected and properly dispose of, or provided for further processing.The water will go back down the drain to the Chrome Recovery process.The oil will be collected and sent back to the mixing tank. A sample ofthis oil will be collected and analyzed for Chrome, moisture, and FFA.The oil that is collected will then be acid washed with a 4%-5% SulfuricAcid solution. The 4%-5% Sulfuric Acid solution will be added to the oilin equal volume,agitated, and then gravity separated.A sample of the oil willbe collected and analyzed for Chrome, Moisture, and FFA. The same samplewill then be centrifuged The sample will then be centrifuged in a tabletop clinical centrifuge to separate any existing water. The oil willthen be siphoned or decanted off the top and analyzed forChrome, Moisture, and FFA. This acid wash step and sample analysis willbe performed three separate times to determine the effectiveness of eachacid wash.This process will then be repeated using Phosphoric Acid for the washstep in place of Sulfuric Acid.

Procedure Update:

A 4th acid wash was performed and the mixture was allowed to settleovernight before separation.

Analysis—Sulfuric Acid Wash DATE: Nov. 20, 2013

SAMPLE ANALYSIS CHROME MOISTURE FFA SAMPLE I.D. (ppm) (%) (%) RAW GREASENo No No Sample Sample Sample 3-PHASE GREASE 7,641.82 15.12% 18% ACIDWASH #1 - RAW 2,969.34 14.83% 34% ACID WASH #1 - CENTRIFUGED 2,237.763.45% 28% ACID WASH #2 - RAW 2,647.01 15.99% 34% ACID WASH #2 -CENTRIFUGED 1,489.41 2.94% 29% ACID WASH #3 - RAW 1,607.04 16.46% 33%ACID WASH #3 - CENTRIFUGED 1,541.25 4.06% 29% ACID WASH #4 - RAW1,314.54 5.62% 30% ACID WASH #4 - CENTRIFUGED 1,274.20 3.67% 29%

Analysis—Phosphoric Acid Wash DATE: Dec. 9, 2013

SAMPLE ANALYSIS CHROME MOISTURE FFA SAMPLE I.D. (ppm) (%) (%) RAW GREASENo No No Sample Sample Sample 3-PHASE GREASE 13,260.51 6.02 20.00 ACIDWASH #1 - RAW 340.28 8.22 34.00 ACID WASH #1 - CENTRIFUGED 47.79 3.7733.00 ACID WASH #2 - RAW 37.78 5.65 33.00 ACID WASH #2 - CENTRIFUGED47.46 3.40 32.00 ACID WASH #3 - RAW 54.44 4.74 33.00 ACID WASH #3 -CENTRIFUGED 47.02 5.07 33.00

Conclusion: The test results confirmed that the following parameters canbe achieved:

A representative summary:

-   -   Settling Tank Stage: >10,000 ppm Chromium    -   Chrome content after 3-Phase: <15,000 ppm    -   Chrome content after acid wash: <50 ppm    -   Chrome content after clarifier: <1 ppm (Estimation)

Further refinements to the process can be made without departing fromthe scope of the invention as claimed herein. The clarifier process stepcan be further refined to achieve less than 1 ppm.

The various chrome recovery examples shown above illustrate a chromerecovery system and process. A user of the present technology may chooseany of the above implementations, or an equivalent thereof, dependingupon the desired application. In this regard, it is recognized thatvarious forms of the subject chrome recovery system and process could beutilized without departing from the spirit and scope of the presentinvention.

As is evident from the foregoing description, certain aspects of thepresent invention are not limited by the particular details of theexamples illustrated herein, and it is therefore contemplated that othermodifications and applications, or equivalents thereof, will occur tothose skilled in the art. It is accordingly intended that the claimsshall cover all such modifications and applications that do not departfrom the spirit and scope of the present invention. Accordingly, thespecification and drawings are to be regarded in an illustrative ratherthan a restrictive sense.

Certain systems, apparatus, applications or processes are describedherein as including a number of modules. A module may be a unit ofdistinct functionality that may be presented in software, hardware, orcombinations thereof. When the functionality of a module is performed inany part through software, the module includes a computer-readablemedium. The modules may be regarded as being communicatively coupled.The inventive subject matter may be represented in a variety ofdifferent implementations of which there are many possible permutations.

The methods described herein do not have to be executed in the orderdescribed, or in any particular order. Moreover, various activitiesdescribed with respect to the methods identified herein can be executedin serial or parallel fashion. In the foregoing Detailed Description, itcan be seen that various features are grouped together in a singleembodiment for the purpose of streamlining the disclosure. This methodof disclosure is not to be interpreted as reflecting an intention thatthe claimed embodiments require more features than are expressly recitedin each claim. Rather, as the following claims reflect, inventivesubject matter may lie in less than all features of a single disclosedembodiment. Thus, the following claims are hereby incorporated into theDetailed Description, with each claim standing on its own as a separateembodiment.

Other aspects, objects and advantages of the present invention can beobtained from a study of the drawings, the disclosure and the appendedclaims.

What is claimed is:
 1. A chrome recovery process comprising the stepsof: steam sparging and mixing oil and solid byproducts from a chrometannery process forming a steam sparged mixture; heating the steamsparged mixture and pumping into a three phase centrifuge separating aseparated oil byproduct; acid washing and agitating the separated oilbyproduct; ceasing agitation and allowing an acid washed oil byproductto separate; heating the acid washed oil byproduct and removing waterfrom the acid washed oil byproduct using a clarifier forming a clarifiedoil byproduct; and capturing the clarified oil byproduct for reuse. 2.The process as recited in claim 1, where heating the steam spargedmixture is heating to about 180 degrees to about 200 degrees Fahrenheit.3. The process as recited in claim 2, where acid washing is about four(4) percent to about five (5) percent acid washing.
 4. The process asrecited in claim 3, where heating the acid washed oil byproduct isheating to about 205 degrees to about 210 degrees Fahrenheit.
 5. Theprocess as recited in claim 1, where the clarifier is a disc typevertical centrifuge.
 6. The process as recited in claim 5, where thecaptured clarified oil byproduct has less than five (5) parts permillion chromium.
 7. A chrome recovery system comprising: a steamsparging mixer having a steam sparger input port communicably connectedto a tannery process byproduct settling tank and operable to receive oilbyproduct and solids byproduct from the tannery process byproductsettling tank into the steam sparging mixer, and said steam spargingmixer having a mixer and steam sparger for mixing and heating the oilbyproduct and the solid byproduct and having an output pump communicablyconnected and adapted to pump a mixed steam sparged byproduct into athree (3) phase centrifuge; and an acid wash agitation vessel having anagitator and an acid infuser and having an agitation vessel input portcommunicably connected to an oil output of the three (3) phase andoperable to receive the oil byproduct into the agitation vessel and saidacid wash agitation vessel having an output pump and communicablyconnected for flowing acid washed oil to a heater and clarifier.
 8. Thesystem as recited in claim 7, where heating the steam sparging mixtureis adapted to heat to about 180 degrees to about 200 degrees Fahrenheit.9. The system as recited in claim 8, where the acid washing agitatorvessel is adapted to provide about four (4) percent to about five (5)percent acid washing.
 10. The system as recited in claim 9, whereheating the acid washed oil byproduct is heating to about 205 degrees toabout 210 degrees Fahrenheit.
 11. The system as recited in claim 7,where the clarifier is a disc type vertical centrifuge.
 12. The system,recited in claim 7, where the clarifier is adapted to capture clarifiedoil byproduct that has less than five (5) parts per million chromium.